The present invention relates to the field of radiotherapy, in particular radiation therapy or radio-surgery. In particular, it concerns producing or updating radiotherapy plans, and here also specifically with radiotherapy plans within the framework of inverse radiotherapy planning.
Work in radiotherapy using inverse planning is computer-assisted, pre-set data being entered into a computer system with respect to the desired dosage distribution in the target area and with respect to the organs to be protected. On this basis, the system is supposed to generate a dosage plan which ensures the best possible treatment. Since for medical reasons, the patient""s therapy in the extra-cranial area is usually fractionated, i.e. radiation exposure is carried out in a number of sessions spaced out in time, it is not guaranteed that the position of the internal organs and of the target area inside the patient correspond to the positions determined in a previous examination of the patient. For this reason, a dosage distribution found to be correct for an earlier session does not for the most part correspond to a correct dosage distribution for a subsequent session.
The correspondence between the positions in the plan and the positions during radiotherapy, however, is relatively good if the patient is not relocated between the point in time at which he is subjected to an imaging procedure and the point in time of radiation exposure. If the patient is scanned again before each radiation exposure, however, new positions for the organs and the target volume result, so that an earlier treatment plan cannot in theory be adopted.
If, however, a new treatment plan is produced for each radiotherapy session, as has been usual to date, the expenditure involved in this is problematic for clinical use. This is because a high expenditure of labour is involved in producing an inverse radiotherapy plan.
A radiotherapy plan should as far as possible have the result that the target volume is completely radiated with the desired dosage; the dosage to the organs to be protected, however, remaining low. Above all in target areas which are relatively close to critical organs, the calculated plan is therefore always a compromise between the dosage distribution of the target volume and of endangered organs. The result of calculating an inverse dosage plan is assessed by way of the dosage-volume histograms. These histograms show what percentage proportion of the volume of a target area or organ absorbs what dosage. How good the resulting compromise can be depends essentially on the position of the target volume relative to the organs to be protected. Whether the calculated inverse plan more protects the critical organs or irradiates the target volume with an almost optimal dosage depends essentially on the pre-set data entered into the planning program.
FIG. 1 shows an embodiment variant for restricting the range in the dosage-volume histograms for the left and right optic nerve. The curve of the finished plan must run below the inserted squares on the left, in order to fulfil the restriction.
FIG. 2 shows an embodiment variant for restricting the range in the dosage-volume histograms for the target volume. The curve of the finished plan must run above the inserted square on the right, in order to fulfil the restriction.
FIG. 3 shows dosage-volume histograms of a calculated inverse plan. Both for the target volume (left) and for the brain stem (right), the course of the curve fulfils the pre-set data (squares).
The pre-set data, which are preferably realised as restrictions of the range for the dosage-volume histograms, are essential to the quality of the resulting plan and heavily dependent on the relative position and size of target volumes and organs to be protected. Accordingly, the high expenditure of labour already mentioned is necessary for producing these pre-set data.
In addition, it is in no way certain that all the pre-set data can actually be kept to by the planning software. Typically, some sort of compromise is proposed in this case. It is therefore not unusual for the pre-set data to have to be iteratively adapted to the result of the plan, and then a new plan has to be calculated. The next, equally work-intensive step is the acceptance (approval) of the plan, preferably by a physician. A plan is only approved when the physician is of the opinion that the compromise found is expedient and could result in as optimal a treatment for the patient as possible. To this end, the physician will preferably consider the dosage-volume histograms, since these provide the best overview of the compromise found.
A further point is that, if a xe2x80x9cfresherxe2x80x9d data set of the patient is recorded before the treatment, the respective target volume and the endangered organs must also be drawn in again for calculating a new plan, since the interior of the patient can shift between the different treatment appointments. This approach, however, causes problems because the expenditure of time and money for recording a data set is relatively high. Not only must the actual target volume be detected but also an adjacent volume, because the knowledge of its radioparency is necessary for dosage planning. It is also necessary to detect a larger volume partly in order to know the position of the markings which are later used for positioning the patient. Furthermore, it is often very unpleasant for an immobilised patient to have to spend a long time between producing a new image data set and radiation exposure, if the new planning takes a long time.
If, a computer tomograph or another X-ray based method is used for recording the new data set, then the patient is exposed to a radiation load roughly proportionally to the detected volume.
It is the object of the present invention to provide a method for producing or updating a radiotherapy plan, which overcomes the above disadvantages. In particular, the expenditure for producing the plan is to be reduced. A further aim of the invention is to enable a new data set to be produced for example every day, within a period of time which is short enough that the patient can remain fixed and immobilised on a treatment bed during this time.
This object is solved in accordance with the invention by a method for producing or updating a radiotherapy plan within the framework of inverse planned radiotherapy, whereby an up-to-date radiotherapy plan is calculated at least partly on the basis of the results of an already existing, approved, older plan. In other words, the information from the older radiotherapy plan which is suitable for xe2x80x9cre-utilisationxe2x80x9d, i.e. which can simplify producing the new radiotherapy plan, is also used for calculating the new radiotherapy plan, in particular inverse calculating with computer-assistance. This deviates from previous practice which discarded the older radiotherapy plan, and in particular through this an inverse plan can be re-calculated with little expenditure of time and labour. In an advantageous embodiment, the dosage distribution of an older, conventionally or inversely produced radiotherapy plan which was found to be xe2x80x9cOKxe2x80x9d is used as a pre-set value for the re-calculation. On the one hand, this means that, the inverse plan can actually with very great probability also be calculated by keeping to all the pre-set values, and on the other hand the dosage distribution considered to be medically appropriate and released by the physician or physicist is (almost) capable of being reproduced.
The pre-set values for calculating the radiotherapy plan can be determined from the results of a previously calculated plan.
In addition, the method invented provides the possibility of possibly also using the knowledge of the approximate form of the target volume and of the organs, in order to reduce the expenditure of time which arises by drawing in the contours.
The third advantage of the method represented here is the reduction in the expenditure of time and money associated with recording a new data record and of the radiation load upon the patient.
Preferred and advantageous embodiments of the method in accordance with the invention are defined by the sub-claims.